High throughput hole forming system with multiple spindles per station

ABSTRACT

A high throughput drilling system for printed circuit board hole formation. Two spindles are disposed at each spindle station, doubling the number of holes produced in a given time period. Each spindle in connected to an overhead linear drive by a mini slide. A first set of the spindles, one for each spindle station, is driven by a first X axis linear drive. A second set is driven by a second X axis linear drive. The work piece table is elongated to support work pieces for all stations, and is supported by a set of bearing guides, with outrigger bearings coupled to the table by flexure mounts that relieve stress due to differential temperature expansion rates between the work piece table and the base table. High speed spindles are employed to obtain higher productivity, with larger holes routed by router tools, eliminating the need for stocking large drill sizes on the system tool changer.

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates to the field of high speed drillingsystems of the type used in the fabrication and population of printedcircuit boards, and more particularly to a high throughput drillingsystem with multiple spindles per station.

BACKGROUND OF THE INVENTION

[0002] Printed circuit boards are typically populated with manysurface-mounted circuit devices. Many small holes are formed in theboards to interconnect the layers of the circuit board. Of course,printed circuit board populated with other types of devices also needholes formed in the boards.

[0003] Drilling machines are typically used to drill the holes in theprinted circuit boards. One exemplary type of system is described inU.S. Pat. No. 4,761,876, the entire contents of which are incorporatedherein by this reference.

[0004] There has been a dramatic increase in the hole count on printedcircuit boards, which makes the cost of drilling the holes a significantpart of the total production cost. In addition, hole sizes are gettingsmaller. Small drills are more expensive and can not be fed with thesame velocity as larger drills. Due to this fact, drilling time and costare further increased.

[0005] It is known the multiple spindles can be employed in a drillingsystem, wherein the spindles are manually positioned in relation to eachother. Manual positioning has the drawback of requiring significantsetup time, to properly position the spindles. Moreover, each time thespindles are required to drill a new part or image, the spindles must bemanually repositioned. This requires a very significant setup time aswell.

[0006] Methods of producing holes by laser are known. However, lasertechnology does not offer a solution for producing large holes and holesthrough multilayer boards.

[0007] It would therefore be an advance in the art to provide a highthroughput drilling system with increased throughput capacity, and whichis capable of forming small as well as larger holes.

[0008] It would further be an advance in the art to provide a machinecapable of mechanically forming larger as well as smaller holes withhigh throughput.

SUMMARY OF THE INVENTION

[0009] A high throughput hole forming system with multiple spindles perspindle station is described. The system includes a base table and awork piece table for supporting work pieces under process. A first drivesystem moves the work piece table along a Y axis in relation to the basetable. The system includes a plurality of spindle stations, each forprocessing at least one work piece. A plurality of sets of spindles areprovided, each spindle for holding a hole forming tool. Each setincludes a spindle at each spindle station. Each set of spindles isbearing mounted on a common linear bearing for linear movement along anX axis which is transverse to the Y axis. The spindles of each set arecommonly connected together to form a ganged spindle set. The systemfurther includes a plurality of computer-controllable spindle lineardrive systems each for commonly driving a set of the spindles along theX axis. A Z axis drive system is provided for individually driving thespindles along a Z axis which is transverse to the X and Y axis.

[0010] The system further comprising a controller for controlling saiddrive systems to conduct hole forming operations on a plurality of workpieces located at respective ones of the spindle stations, such that aspindle of each set is operated to conduct hole forming operationssimultaneously on a single work piece at a given station.

[0011] In accordance with another aspect of the invention, a method isdescribed for forming holes in a work piece, comprising a sequence ofthe following steps:

[0012] providing a spindle capable of very high rotational drive ratesand a linear drive, for rotating a tool and feeding the tool into andout of a work piece;

[0013] providing a selection of tools including a set of drilling toolsof various diameters, and at least one router tool;

[0014] using one or more tools of the set of drilling tools to drill aset of holes in a work piece having diameters less than a predeterminedthreshold size; and

[0015] using said router tool to form one or more holes of diameterslarger than the threshold in a routing operation.

BRIEF DESCRIPTION OF THE DRAWING

[0016] These and other features and advantages of the present inventionwill become more apparent from the following detailed description of anexemplary embodiment thereof, as illustrated in the accompanyingdrawings, in which:

[0017]FIG. 1 is a front view of a multiple spindle per station drillingsystem embodying the invention.

[0018]FIG. 2 is a side view of the drilling system of FIG. 1.

[0019]FIG. 3 is an isometric view of the X-axis drive system of thesystem of FIG. 1.

[0020]FIG. 4 is a simplified front view of the system of FIG. 1,illustrating the elements used in guiding the work piece table.

[0021]FIG. 5 shows one of the outrigger flexure mounts in furtherdetail.

[0022]FIG. 6 illustrates an exaggerated compliance condition of theoutrigger flexure mounts due to differential thermal expansion betweenthe work piece and base tables and bearing rail misalignment.

[0023]FIG. 7 shows a partially broken-away front view of exemplary slide104 and the mounting structure which mounts the spindle 76 to the slide.

[0024]FIG. 8 is a partially broken-away side view of the structure ofFIG. 7.

[0025]FIG. 9 is a partially broken-away top view of the structure ofFIG. 7.

[0026]FIG. 10 shows in a simplified isometric view the use of a routertool to form a hole in accordance with an aspect of the invention.

[0027]FIG. 11 is a simplified diagrammatic diagram of the control systemfor the system.

[0028]FIG. 12 is a simplified isometric view of a multiple spindle holeforming operation on a multiple image work piece.

[0029]FIG. 13 is a simplified diagrammatic illustration of an alternateX-axis drive system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0030] In accordance with one aspect of the invention, a multiplespindle per station drilling system is described. An exemplaryembodiment is illustrated in FIG. 1 as drilling system 50, and providedtwo spindles per station. Using two spindles per station produces alarge gain in productivity over conventional systems, since the samenumber of holes can be produced in half the time, assuming that multipleimages are used in producing the board. Multiple images on a boardrepresents the norm, not the exception, in today's production of printedcircuit boards. Therefore, adding a second spindle to each station willcontribute significantly to machine productivity. There are additionalbenefits to utilizing this type of new system architecture. For example,the number of tool change cycles can be reduced by 50%, because the twospindles are changing drills at the same time.

[0031] This invention is not limited to applications employing twospindles per spindle station, as it is contemplated that three, four,six or more spindles per station can be employed, each with anindependent X-axis drive system.

[0032] A problem in a multiple-spindle per station approach is theincreased complexity of the system, making it difficult to obtain lowcost objectives. In accordance with another aspect of the invention, thesystem employs a set of mini slides, each carrying one spindle each,connected by push rods, to allow a single servo drive to position fourspindles along the X axis. A second set of mini slides and servo driveis used to position a second set of four spindles along the X axis. Alleight mini slides travel on a pair of rails attached to the overheadbeam of the system. This simplifies the X positioning system to make themultiple-spindle per station architecture economically feasible, andimproves machine dynamics by reducing moving mass dramatically.Moreover, because the spindles for each station often are moved inopposite directions, the respective movements tend to cancel theacceleration forces set up in moving the spindles and thus help tostabilize the machine.

[0033]FIG. 1 shows a drilling system 50 embodying the multiple-spindleper station architecture in accordance with the invention. In thisexemplary embodiment, the system has four stations 60A-60D, and eachstation is served by two spindles each. Thus, in this embodiment,spindles 62 and 64 serve station 60A, spindles 66 and 68 serve station60B, spindles 70 and 72 serve station 60C, and spindles 74 and 76 servestation 60D. The spindles can be moved by spindle drive systems up anddown along the Z axis under control of the system controller to feed thedrilling tool into and out of the work pieces, which are carried on atable 80, shown generally in the side view of FIG. 2. The drillingsystem 50 further includes a table drive for moving the work piece table80 along the Y axis. The spindles are mounted on slides carried on theoverhead beam 82 for movement along the X axis. All the foregoingelements are supported on a granite base table 150, with the overheadbeam 82 supported above the base table and the work piece table 80 byleft and right uprights 152 and 154.

[0034] As further shown in FIG. 1, the system 50 employs a system ofgrippers and tool magazines adapted to permit automated tool changing ofthe tools put to use by each spindle. The grippers 180A-180H are carriedalong the forward edge of the table 80 in a spaced arrangement, with onegripper being provided for each spindle. Each spindle also has mountedthereto a tool magazine, which is therefore also positionable in X-axisby the X-axis drive system, and in the Z-axis by the spindle Z-axisdrive. By coordinated movement of the table drive, the X-axis drive andthe Z-axis drive systems, a given spindle may be aligned over itsgripper, and lowered to place the tool in position in the spindle in thegripper. The gripper is then actuated to grip and hold the tool. Thespindle is then moved in X and Y to position the tool magazine over thegripper to receive in an empty receptacle the tool removed from thespindle and now held by the gripper. Thereafter, the tool magazine isagain repositioned to align a fresh tool over the gripper, now empty.The gripper picks the fresh tool, the tool magazine is moved away, andthe spindle now moved over the gripper to take the fresh tool. The toolcan be operated in the spindle at a laser runout check station, e.g.station 186A, and then another hole forming operation can proceed. Thistool changing system is similar to the system described in U.S. Pat. No.5,068,958, “Method and Apparatus for Changing Tools in an AutomatedMachine Tool,” except that the magazines are carried by the spindlesinstead of by the overhead beam. Grippers and tool magazines suitablefor the purpose are described in this patent, the entire contents ofwhich are incorporated herein by this reference.

[0035] An advantage of the system is that tool changing operations forall spindles, including all spindles at each station, can be conductedsimultaneously, thus reducing the amount of time needed for toolchanging.

[0036]FIG. 2 is a right side view of the drilling system of FIG. 1, andfurther illustrates the arrangement of the architecture of the system. AY-axis table drive system is employed to position the table along the Yaxis. This drive system includes a servo motor 88A driving a leadscrew88B, with the leadscrew nut (not shown) attached to the table 80. ThisY-axis drive system is a conventional drive system.

[0037] The Y-axis table drive system moves the work piece table 80precisely back and forth along the Y axis to precisely position the workpieces in one axis with respect to the spindles 62-76.

[0038]FIG. 3 is a functional diagram of the X-axis drive system for thesystem 50, which precisely positions the spindles along the X-axis Eachspindle has a Z-axis drive system mounted to a slide structure, andsince there are eight spindles for the system of FIG. 1, there are alsoeight slide structures, with each station having a primary slidestructure and a secondary slide structure. Thus, station 60A hasassociated therewith primary slide structure 90 and secondary slidestructure 92, station 60B has primary slide structure 94 and secondaryslide structure 96, station 60C has primary slide structure 98 and 100,and station 60D has primary slide structure 102 and secondary slidestructure 104. For clarity, only one Z-axis spindle drive 62A (forspindle 62) is illustrated in a block form; the remaining spindle drivesare not shown in FIG. 3.

[0039] The slide structures are each mounted on three roller guidingbearings for sliding movement along bearing guiding rails 84 and 86which are mounted to the granite overhead beam 82. The rails 84 and 86extend along the X-axis. Each slide structure has secured thereto twolower roller bearing slides for engaging the lower rail 84 and one upperroller bearing slide for engaging the upper rail 86. For example, slide92 is secured to the lower rail 84 by lower roller bearing slides 92Band 92C, and to the upper rail 86 by upper bearing slide 92A. With theguiding rails and roller guiding bearings, the slide structures are allconstrained for movement only along the X-axis. The roller guidingbearings are preloaded to increase stiffness and eliminate lost motion,improving guiding accuracy.

[0040] The system 50 includes two X-axis drive systems, one for drivingthe primary slide structures and the corresponding primary spindles, theother for driving the secondary slide structures and the correspondingsecondary spindles. In this exemplary embodiment, each drive is aleadscrew drive. The primary slide structures are all ganged together byconnection to primary spindle actuator bars 110 and 112, such that theprimary slide structures 90, 94, 98 and 102 move in unison along theX-axis. The secondary slide structures are all ganged together byconnection to secondary spindle actuator bars 114 and 116, such that thesecondary slide structures 92, 96, 100 and 104 move in unison along theX-axis.

[0041] The primary spindle drive 120 includes the leadscrew 120A, motordrive 120B mounted within leadscrew housing 120C to the overhead beam80, and the common primary drive attachment 120D, a leadscrew nut. Thenut 120D is attached to one of the primary slide structures, in thisembodiment to slide structure 94. This slide structure in turn pulls theother three slides 90, 98 and 102 along due to the common connection viathe spindle actuator bars 110, 112. In a conventional manner, theleadscrew servo motors are attached to the leadscrews through couplings,e.g. coupling 120E (FIG. 1).

[0042] The secondary spindle drive includes the leadscrew 122A, motordrive 122B mounted within leadscrew housing 122C to the overhead beam80, and the common secondary drive attachment nut 122D, attached tosecondary slide structure 100.

[0043]FIG. 4 is a simplified front view of the system 50, illustratingonly elements used in guiding the work piece table 80. The table 80 inthis exemplary embodiment is a laminated steel table, supported formovement along the Y axis by a master linear roller bearing 160positioned centrally along the length of the table, i.e. centrally alongthe Y axis extent. Thus, a linear roller bearing slide 160A is securedto the undersurface 80A of the table 80, and a linear roller guidingrail 160B is secured to the base table 150. The bearing slide ispreloaded against the rail to increase stiffness and improve accuracy.The rail 160B guides the top structure along a constrained linear pathwhich extends along the Y axis.

[0044] Further supporting and guiding the table 80 as it is moved alongare left and right outrigger linear roller bearings 162 and 164 whichare positioned adjacent the left and right table ends 80L and 80R. Thesebearings include the front linear roller slides 162A and 164A, the rearlinear roller slides 162C and 164C, (FIG. 2) and guiding rails 162B and164B.

[0045] Since the system 50 has eight spindle stations, the table 80 hasa considerable length along the Y axis to support work pieces processedby the different spindle stations. In this exemplary embodiment, thislength is 96 inches. Because the table 80 is laminated steel, and thetable 150 is granite, there will be differentials in the respectivethermal expansion coefficients of the tables. With the table supportedand constrained for movement along linear rails at each end 80L and 8ORwhich extend along the Y axis, the linear roller 160, 162 and 164provide extremely high guiding tolerances. The differential in thermalexpansion rates of the tables over the temperature operating range ofthe system would create enormous stress on the bearings. This stresswould result in bearing damage if the stress could not otherwise berelieved. Stress relief is provided in the following manner.

[0046] Outrigger flexure mounts 168 and 170 are employed to connect therespective front roller bearing slides 162A and 164A and the rear rollerbearing slides 162D and 164D to the bottom surface 80A of the table 80.These flexure mounts are fabricated of a spring steel material. FIG. 5shows flexure mount 170 in further detail; the other three flexuremounts are identical. The flexure mount has a generally I-shapedcross-section configuration. A flat top web portion 170A is secured tothe bottom surface of the table by threaded fasteners. A flat bottom webportion 170B is connected to the bearing slide 164A, e.g. also bythreaded fasteners. The top and bottom web portions are joined by amiddle web portion 170C. The middle web portion has a relatively largethickness in the central part 170D, but a relatively thin dimension at170E and 170F where the middle web portion connects to the top andbottom web portions, respectively. These relatively thin areas allow themount 170 to flex or comply in response to differential thermalexpansion rates between the work piece table 80 and the lower table 150,or to compensate for bearing rail misalignment. In an exemplaryembodiment, the middle web portion 170C has a height of 2.5 inches, withthickness dimensions of 0.260 inches at the web region 170D and 0.093inches at web regions 170E and 170F.

[0047]FIG. 6 illustrates an exaggerated compliance condition of theoutrigger flexure mounts due to differential thermal expansion betweenthe tables 80 and 150. Assume that the table 80 has a higher expansionrate than the lower table 150. Instead of developing stress in theoutrigger guide bearings, the flexure mounts flex at the regions ofreduced thickness, as illustrated in exaggeration in FIG. 6. At the sametime, the flexure mounts maintain stiffness in the Y and Z directions.

[0048] The spindles are mounted to the respective slides by a mountingstructure employing a set of wedges, more particularly described inFIGS. 7-9. FIG. 7 shows a partially broken-away front view of exemplaryslide 104 and the mounting structure which mounts the spindle 76 to theslide. One function of the wedge structure is to bring the spindlecenter line in line with the primary spindle 74 and X-axis travel.Another function is to make the spindle 74 perpendicular to the toptable.

[0049] Each spindle drive assembly is carried by the X-axis guideassembly which includes the rails 84 and 86. Each spindle guide assemblymounting plate (plate 200 in FIG. 7) is attached to the correspondingX-axis slide (slide 104 in FIG. 7) through three threaded fasteners(fasteners 202A-200C in FIG. 7). Each fastener is threaded through aslot in a corresponding wedge block which acts on a correspondingincline surface formed in the slide. The wedges can be moved up and downthe incline plane surfaces.

[0050] There are three fasteners and wedges to provide a three-pointsuspension for the spindle mounting plate. As shown in the sidecross-sectional view of FIG. 8, fastener 202A is threaded through a slot210A formed in wedge block 204A, which acts on incline surface 104F.Fastener 202B is threaded through slot 210B formed in wedge block 204B,which acts on incline surface 104G. While not visible in FIG. 8,fastener 202C is threaded through a slot 210C formed in wedge 204C,which acts on incline surface 104H. The top wedge and bottom wedges arereversed in direction for easy access to adjustment set screws206A-206C. The adjustment set screws 206A-206C are captured in cutouts208A-208C slightly larger than the lengths of the set screw andequivalent in width to ⅛ diameter. In the wedge there is a one halfdiameter threaded hole which will propel the wedge up and down dependingon the direction the set screw is turned.

[0051] The wedges can be moved by the set screws. By rotating the setscrews, the wedges are forced to move in the incline defined by theincline surfaces. This movement causes the spindle plate to move frontto back in the of the wedge which is being manipulated. Moving eachwedge in different amounts allows the tilt of the spindle plate to beadjusted. By moving each wedge the same amount in the proper direction,the front to back location of the spindle plate can be adjusted. Thewedges and set screws are under constant compression load during theadjustment. The compression load is applied by wave springs 208A-208Cwhich are located under each mounting bolt head. When all adjustmentsare complete, the spindle plate is locked down to the carriage plate bytightening the bolts which attache the spindle plate to the slide.

[0052] This method of attachment of the spindle drive mounting plates tothe slides allows the alignment of two spindles working on one stationin line with the X-axis travel. This also allows correction forperpendicularity of the spindle to the table so. Thus, the spindle platemounting structure shown in FIGS. 7-9 is used to adjust a spindle sothat its centerline would be perpendicular to a plate on the table 80which would hold a piece of material that the spindle would drill.

[0053] It is further necessary to adjust the relative position of eachsecondary spindle to the corresponding primary spindle along the X axis.This can be accomplished by drilling a hole with each spindle at a knownprogrammed distance, and measuring the distance between the drilledholes and comparing the measured value to the programmed value to obtainan error distance. The adjustment to correct the error distance isaccomplished by untightening the slide of one of the spindles from theactuator rods, and adjusting the spindle location, monitoring thedistance moved with a dial indicator of proper measurement accuracy.When the error adjustment is complete, the slide is reattached to theactuator rods.

[0054] To further increase the system throughput according to a furtheraspect of the invention, the spindles 62-76 include high RPM spindledrives. In an exemplary embodiment, the spindle drives operate at amaximum rate of 150,000 RPM. This is in contrast with typical drillingspindle maximum rates on the order of 110,000 RPM. Use of high RPMspindles allows faster feed rates and prolongs drill life. A faster feedrate will improve machine productivity considerably, in some cases by25% or more. High RPM spindle drives suitable for the purpose areavailable commercially.

[0055] A problem with such high RPM spindles is that they do not havesufficient power to reliably produce large holes, say larger than 0.125inches. Moreover, the high speed spindles available today are incapableof producing large holes because the linear thrust bearings employed inthe spindles are inadequate. In accordance with a further feature of theinvention, such large holes are produced by the system by a routingtechnique using a router tool. All holes larger than a given thresholdsize, e.g. 0.1249 inches, are produced by the routing technique. Thereare many router tools that could be employed for this purpose. It isdesirable that the outer diameter of the router tool be controlled to atight tolerance. For an exemplary embodiment, the router tool outerdiameter is 0.062 plus/minus 0.002 inches.

[0056] A laser diameter check determines router size, and applies theproper offset to compensate for size and bit defection. Laser equipmentsuitable for the purpose is well known in the art.

[0057]FIG. 10 shows in a simplified isometric view the use of a routertool to form a hole in accordance with this aspect of the invention.Here, exemplary high speed spindle 62 carries a router tool 220. Insteadof producing a hole by simply feeding the tool into the work piece 10vertically down and then up along the Z axis in a typical drillingsequence, a routing sequence is employed. The tool is still fed into thework piece vertically to route a small hole, and then, with the spindlein the down position and the tool rotating at high speed, moved in X andY through a spiral path. The spiral path results in the formation of alarger hole than the diameter of the tool 220, and yet still forms tinychips instead of a plug of material. The spiral path is achieved bymotion of the spindle and table 80 in X and Y to create the spiralmotion of the router tool.

[0058] Forming large holes using this routing technique will eliminatethe need for stocking large diameter drill sizes, since all large holes,e.g. holes with diameters exceeding 0.125 in an exemplary embodiment,will be formed with a single router tool. A tool diameter size suitablefor the purpose is 0.062 inches. It is desirable that the outer diameterof the router tool be controlled to a tight tolerance. For thisexemplary embodiment, the router tool outer diameter is 0.062 plus/minus0.002 inches. In addition, tool changes for large drills will beeliminated, since a single router tool can be used.

[0059]FIG. 11 is a simplified diagrammatic diagram of the control systemfor the system 50. The control system includes a system control unit300, an interface unit 302, a primary X-axis servo amplifier 304, asecondary X-axis servo amplifier 306, a Y-axis servo amplifier 308, anda spindle control unit 310. The amplifier 304 provides drive signals tothe primary servo drive motor 120B. The amplifier 306 provides drivesignals to the secondary servo drive motor 122B. In addition, each servoamplifier receives position feedback signals.

[0060] The spindle control unit provides control signals to the spindlerotary drive motors 62A-76A and to the linear motors 62B-76B whichprovide Z-axis drive to the spindles. In addition, the spindles eachhave velocity and position feedback sensors, e.g. velocity sensor 62Cand position sensor 62D for spindle 62.

[0061]FIG. 12 is a simplified isometric view of a multiple spindle holeforming operation on a multiple image work piece. Here the work piece isa stack of three identical panels 10A-10C, each having 24 identicalimages 12 formed thereon. The spindles are positioned and controlled tosimultaneously form identical holes on corresponding locations in therepeated images. To simplify tool changing and movement of the primaryand secondary X-axis drives, each spindle is using identical tools toform corresponding holes in the images. With three panels stacked, threepanels are processed simultaneously.

[0062] The controller software control takes input data specifyinglocations and sizes of all holes to be formed for the work piece, andassigns holes to each spindle, as well as the sequence in forming theholes. In general, the work piece is divided into two halves, and holeson one side are assigned to the spindle for that half of the work piece,although holes in a central region can be assigned to either spindle.The controller software control also includes anti-collision functionsto ensure that adjacent spindles do not collide during hole formingoperations.

[0063] The drilling system described herein provides significantproductivity improvements as compared to known four spindle systems.This can be illustrated by the following example. Consider a typicalprinted circuit board panel, having 12,000 holes to be formed, with 12different hole sizes. There would typically be 20 tool changes,including 8 drill changes of the same size tool, consuming about 10minutes. With an average hit rate of 150 per minute, the running timefor the panel will be about 80 minutes, i.e. 70 minutes for drilling and10 minutes for the tool changes.

[0064] With the new machine, with two spindles per station, the runningtime for hole drilling/forming will be cut in half, from 70 minutes to35 minutes. The time required for tool changing is reduced, e.g. from 10minutes to 6 minutes, thus providing a total running time of 41 minutes.This is just the productive improvement contribution from using twospindles per station.

[0065] Using a high RPM spindle at each station provides a furtherproductivity improvement. An exemplary 150,000 RPM spindle speed willprovide a drill cycle time reduction of about 28% in one example. Thiscould reduce the 35 minute drill running time computed above by 9.8minutes. This would produce a 25.2 minute drill running time, plus the 6minute tool changing time, or a total running time of 31.2 minutes.

[0066] Using a router tool to form all large diameter holes produces afurther productivity improvement. In a typical board panel, several toolchanges could be eliminated, perhaps as many as 8, reducing toolchanging time by as much as 4 minutes. This could further reduce thetotal running time to 31.2 minutes minus 4 minutes, to 27.2 minutes.

[0067] In an alternate embodiment, the X axis spindle drive is actuatedby a linear electric motor drive. This embodiment is illustrated in FIG.13. Here the primary leadscrew drive of FIG. 3 has been replaced with alinear motor including stationary magnet assembly 260 which interactswith coil assemblies secured to each primary slider 90, 94, 98 and 102.Only coil assembly 262 secured to slider 94 is shown in FIG. 7.Similarly, the secondary leadscrew drive of FIG. 3 has been replacedwith a linear motor including stationary magnet assembly 270 whichinteracts with coil assemblies secured to each secondary slider 92, 96,100, 104. Exemplary coil assembly 272 is shown as secured to slider 100in FIG. 13. The advantages of a linear motor in relation to a leadscrewdrive include the increased stiffness of the linear motor, allowing thesystem to be driven faster and more accurately. Also, there are nocomponents to wear out in a linear motor, in comparison to themechanical leadscrew components.

[0068] It is understood that the above-described embodiments are merelyillustrative of the possible specific embodiments which may representprinciples of the present invention. Other arrangements may readily bedevised in accordance with these principles by those skilled in the artwithout departing from the scope and spirit of the invention.

What is claimed is:
 1. A high throughput hole forming system withmultiple spindles per spindle station, comprising: a base table; a workpiece table for supporting work pieces under process; a first drivesystem for moving the work piece table along a Y axis in relation to thebase table; a plurality of spindle stations; a first set of spindles,each for holding a hole forming tool, comprising a first spindle at eachsaid spindle station; a second set of spindles, comprising a secondspindle at each said spindle station; a first spindle linear drivesystem for commonly driving said first set of spindles along an X axiswhich is orthogonal to said Y axis; a second spindle linear drive systemfor commonly driving said second set of spindles along the X axis; and Zaxis drive system for driving said spindles along a Z axis which isorthogonal to said X and Y axis.
 2. The system of claim 1 furthercomprising a controller for controlling said Y axis, X axis and Z axisdrive systems to conduct hole forming operations on a plurality of workpieces located at respective ones of said spindle stations, such that afirst spindle of said first set and a first spindle of said second setis operated to conduct hole forming operations simultaneously on asingle work piece.
 3. The system of claim 1 wherein said first set ofspindles and said second set of spindles are arranged on a common planewhich is orthogonal to said work piece table.
 4. The system of claim 1wherein spindles of said first set are interleaved along the X axis withspindles of the second set.
 5. The system of claim 1 wherein said firstspindle linear drive includes: a linear bearing for supporting a firstset of spindle slides for motion along the X axis, each slide supportinga corresponding one of said first spindle set; a first bar structurerigidly attached to each slide of said first slide set to gang togethersaid first set of slides in a spaced relationship on said linear bearingfor motion as a first ganged set along the linear bearing; and a firstlinear force applying structure for moving the first ganged set alongthe X axis.
 6. The system of claim 5 wherein said first linear forceapplying structure includes a servo motor coupled to a leadscrew, and aleadscrew nut threaded onto the leadscrew and secured to said firstganged set.
 7. The system of claim 6 wherein said leadscrew nut issecured to one slide of said first set of slides.
 8. The system of claim5 wherein said first linear force applying structure includes a linearmotor drive system including a set of stationary permanent magnetsextending along the X axis and a coil attached to said first ganged set.9. The system of claim 5 wherein said linear bearing further supports asecond set of spindle slides for motion along the X axis, each slide ofsaid second slide set supporting a corresponding spindle of said secondspindle set, and wherein second spindle linear drive further includes: asecond bar structure rigidly attached to each slide of said second slideset to gang together said second set of slides in a spaced relationshipon said linear bearing for motion as a ganged set along the linearbearing; and a second linear force applying structure for moving thesecond ganged set along the X axis.
 10. The system of claim 5 whereinsaid linear bearing includes first and second linear guiding railssecured to an overhead beam supported over said work piece table, and,for each slide, a plurality of bearing slide members each attached tosaid slide and constrained for sliding movement along one of said linearguiding rails.
 11. A hole forming system for forming holes in a workpiece under automated control, comprising: a base table; a work piecetable for supporting work pieces under process; a Y axis drive systemfor moving the work piece table along a Y axis in relation to the basetable; a spindle including a rotary drive for rotating a tool at veryhigh speed during hole forming operations; an X axis drive system fordriving said spindle along an X axis which is orthogonal to said Y axis;Z axis drive system for driving said spindle along a Z axis which isorthogonal to said X and Y axis; a tool changer for holding one or moredrilling tools and a router tool for selective use in the spindle duringhole forming operations; a controller for controlling the X axis, Y axisand Z axis drive systems, said spindle rotary drive and said toolchanger for selecting an appropriate tool for hole forming operationsand executing said hole forming operations, wherein said system iscontrolled to use a drilling tool to form holes having an outer diameterunder a predetermined threshold diameter by rotating the drilling toolat very high speed and feeding the drilling tool into and out of thework piece along a single Z axis, and to use a router tool to form holeshaving an outer diameter exceeding the threshold diameter by a routingmovement.
 12. The system of claim 11 wherein said spindle is capable ofrotary spindle rates of 150,000 revolutions per minute.
 13. The systemof claim 12 wherein said predetermined threshold diameter is about 0.125inches.
 14. The system of claim 11 wherein said routing movementincludes a spiral movement of the rotating router in a plane transverseto the Z axis.
 15. The system of claim 11 wherein a single router toolis employed to form all holes having a diameter exceeding said thresholddiameter, thereby minimizing tool changes.
 16. A method for formingholes in a work piece, comprising a sequence of the following steps:providing a spindle capable of very high rotational drive rates and alinear drive, for rotating a tool and feeding the tool into and out of awork piece; providing a selection of tools including a set of drillingtools of various diameters, and at least one router tool; using one ormore tools of the set of drilling tools to drill a set of holes in awork piece having diameters less than a predetermined threshold diametersize; and using said router tool to form one or more holes of diameterslarger than the threshold diameter in a routing operation.
 17. Themethod of claim 16 wherein said routing operation includes feeding therotating router tool into the work piece, with the tool still rotatingin the work piece, providing relative movement between the tool and thework piece to move the router tool through a path transverse to thespindle axis.
 18. The method of claim 17 wherein the transverse path isa spiral path.
 19. The method of claim 16 wherein said spindle iscapable of rotary spindle rates of 150,000 revolutions per minute. 20.The method of claim 19 wherein said predetermined threshold diameter isabout 0.125 inches.
 21. A hole forming system for forming holes in aplurality of work pieces, comprising: a base table; an elongated workpiece table for simultaneously supporting a plurality of work piecesdistributed along a longitudinal extent of the work piece table; abearing system for supporting the work piece table for constrainedmovement of the work piece table along a first axis which is transverseto said longitudinal extent; a table drive system for driving the workpiece table along the first axis under computer control; the bearingsystem including first and second outrigger bearings for supporting thework piece table at respective outrigger positions adjacent oppositeends of the table, and respective first and second flexure mountstructures for coupling the work piece table to the first and secondbearings, said flexure mount structures for providing stiffness indirections transverse to said first axis while having flexibility fordisplacement along the first axis in response to stress forces directedalong the longitudinal extent, thereby relieving forces resulting fromdifferential thermal coefficients of expansion of the respective tableor bearing misalignment.
 22. The system of claim 21 wherein said bearingsystem includes first and second linear guiding rails attached to saidbase table and extending in parallel to the first axis, and first andsecond bearing slides attached to said flexure mount structures forrespectively engaging the first and second rails.
 23. The system ofclaim 21 wherein the flexure structures each comprise an integralstructure formed of a springy material, the structure having across-section configuration in the general form of an I, wherein top andbottom web portions are connected by a middle web portion, and whereinthe middle web portion has first and second spaced regions of reducedthickness, wherein the flexure structures are flexible at said regionsof reduced thickness.
 24. A high throughput hole forming system withmultiple spindles per spindle station, comprising: a base table; a workpiece table for supporting work pieces under process; a first drivesystem for moving the work piece table along a Y axis in relation to thebase table; a plurality of spindle stations; a plurality of sets ofspindles, each spindle for holding a hole forming tool, each setincluding a spindle at each said spindle station, each set of spindlesbearing mounted on a common linear bearing for linear movement along anX axis which is transverse to said Y axis, the spindles of each setcommonly connected together to form a ganged set; a plurality ofcomputer-controllable spindle linear drive systems each for commonlydriving a set of said spindles along said X axis; and Z axis drivesystem for individually driving said spindles along a Z axis which istransverse to said X and Y axis.
 25. The system of claim 24 furthercomprising a controller for controlling said drive systems to conducthole forming operations on a plurality of work pieces located atrespective ones of said spindle stations, such that a spindle of eachset is operated to conduct hole forming operations simultaneously on asingle work piece at a given station.
 26. The system of claim 24 furthercomprising adjustable mounting structure for mounting each spindle tosaid bearing system to align each spindle in the Z and X axis.